Electron discharge device circuit



Feb. 18, 1941. w. R. KOCH ELECTRON DISCHARGE DEVICE CIRCUIT FREQUENCY M x F 5 y 00, H m M F we a 0/3 w 3 40/ 2 5 FM Wm #7 a muwQwkg.

Patented Feb. 18, 1941 UNITED STATES PATENT OFFICE Winfield R. Koch, Haddonfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application July 22,

6 Claims.

This invention relates to electron discharge device circuits such as are utilized to neutralize the effect of the capacity coupling between the electrodes of the device, and has for its principal object the provision of an improved neutralizing or compensating circuit whereby the inter-electrode impedance of such devices is maintained substantially constant over a, relatively wide band of frequencies and whereby a more satisfactory phase relation is maintained between the input and output potentials of the device.

A customary method of compensating for the capacity coupling between the input and output electrodes of an electron discharge device is disclosed by Nichols U. S. Patent 1,325,879. This method involves the provision of an inductor and a direct current stop condenser which are series connected between the input and output electrodes so that, instead of a capacity coupling between the grid and anode electrodes, there is provided a parallel circuit which presents a high impedance and operates with zero phase shift so long as the carrier frequency does not vary. At frequencies somewhat off resonance, however, the phase shifts produced in the output and input circuits are likely to permit the generation of oscillations due to feedback from the output circuit.

In accordance with the present invention, this difficulty is minimized by the provision of (1) a circuit resonant to the mid frequency of the frequency band to be passed by the electron discharge device, and (2) a resistor which is connected through this mid-frequency resonant circuit in shunt to the inductor of the aforesaid patent. As will appear, this improved compensating network has the advantage that the interelectrodeimpedance of the device and the phase relation between its input and output currents are .maintained substantially constant over a relatively wide range of frequencies. Otherwise stated, the anode-to-grid impedance is made resistive over a relatively wide band of frequencies.

The invention will be better understood from the following description considered in connection with the accompanying drawing, and its scope is indicated by the appended claims.

Referring to the drawing,

Figure 1 is a wiring diagram of a prior art compensating circuit,

Figures 2, 3 and 4 illustrate different modifications of the invention, and

Figure 5 is an explanatory diagram relating to the operation of the invention.

The prior art wiring diagram of Fig. 1 in- 1939, Serial No. 285,905

eludes an electron discharge device I0 which is provided with a tuned input circuit 1 I comprising a control grid electrode I2 and a tuned output circuit I3 comprising an anode or plate electrode a capacity coupling which is indicated by the dotted lines l5, the effect of this coupling being neutralized at a particular frequency by an inductor l6 which is connected between the electrodes l2 and I4 through a direct current stop condenser IT. This compensating circuit, as previously indicated, has the disadvantage that changes in impedance between the electrodes l2 and I4 and in the phase relation between the input and output currents may result in the generation of oscillations due to the feedback of energy to the input circuit. Thus, assuming the desired frequency band to be as indicated in Fig. 5, it will be noted that the inter-electrode impedance variation represented by the curve A is very considerable within the desired frequency range, and that the phase relation change between the input and output currents represented by the curve B is also relatively large within this frequency range.

This disadvantage is obviated by the circuit of Fig. 2, which differs from that of Fig. 1 in that a resistor l8 and a circuit l9-2ll are series connected in shunt to the inductor I6, this circuit I920 being series resonant to the mid-point of the frequency band to be passed by the device Ill. The effect of this circuit is shown in Fig. 5, the curve C indicating the inter-electrode impedance and the curve D indicating the phase relation change with this improved circuit. It will be noted that both the impedance and phase relation remain substantially constant throughout the desired frequency range.

A still wider frequency range may be utilized without danger of oscillations if the series resonant circuit of Fig. 2 is replaced by the parallel resonant circuits 2l-22 and 2324, of Fig. 3. In this modification, one of the parallel resonant circuits is preferably tuned to a frequency above the desired band and the other to a frequency below the desired band.

Another form of the compensating network, particularly useful where it is desired to operate over a considerable band of frequencies, is that of Fig. 4, wherein the resistor I8 is shunted by the parallel resonant circuits 25-26 and Z l28 and is series connected with the series resonant circuits 29-30 and 31-32 which are shunted to a series resonant circuit 33-34.

Between the electrodes l2 and I4 there exists 6 This circuit offers a. somewhat lower effective impedance between grid and anode, but the impedance can be made uniform over the band instead of following'the double-peak curve shown in Fig. 5, with the phase angle substantially zero. The circuits all tune to the mid-band frequency. The ratio of the series-circuit inductances to the inductance l6 depends on the band-width. For a particular band, inductance 29 should equal inductance 3| and be .89 times inductance 33. Inductance 25 should be equal to inductance l6 and be 2.25 times inductance 21. How the circuit constants to be. used may be determined, in view of the particular conditions under which the circuit is to be utilized, is apparent in view of the foregoing explanation.

I claim as my invention:

1. The combination of an electron discharge device including input and output electrodes between which a capacitative coupling tends to exist, and a compensating network including an inductor connected between said electrodes, a series resonant circuit, and a resistor connected in shunt to said inductor through said series resonant circuit.

2. The combination of an electron discharge device including input and output electrodes between which a capacitative coupling tends to exist, and a compensating network including an inductor connected between said electrodes, a parallel resonant circuit, and a resistor connected in shunt to said inductor through said parallel resonant circuit.

3. The combination of an electron discharge device including input and output electrodes between which a capacitative coupling tends to exist, and a compensating network including an inductor connected between said electrodes, a circuit resonant to the mid-frequency of the frequency band to be passed by said device, and a resistor connected in shunt to said inductor through said circuit.

4. The combination of an electron discharge device including input and output electrodes between which a capacitative coupling tends to exist, and a compensating network including an inductor connected between said electrodes, a series circuit resonant to the mid-frequency of the frequency band to be passed by said device, a parallel circuit resonant to said mid-frequency and connected in shunt to said inductor through said series resonant circuit, and a resistor connected in shunt to one of said resonant circuits.

5. The combination of an electron discharge device including input and output electrodes between which a capacitative coupling tends to exist, and a compensating network including an inductor connected between said electrodes, 9. series circuit resonant to the mid-frequency of the frequency band to be passed by said device, a parallel circuit resonant to said mid-frequency and connected in shunt to said inductor through said series resonant circuit, and a resistor connected in shunt to said parallel resonant circuit.

6. In a signal transmission system responsive to a predetermined frequency band, the combination of an electron discharge device including input and output electrodes between which a capacitative coupling tends to exist, and a compensating network including an inductor connected between said electrodes, a pair of parallel resonant circuits, one of said circuits being tuned to a frequency above the mean frequency of said band and the other of said circuits being tuned to a frequency below the mean frequency of said band, and a resistor connected in shunt to said inductor through said parallel resonant circuits.

WINFIELD R. KOCH. 

